Biomedical subjects

Eloy A Villegas

Publications and source records attributed to Eloy A Villegas.

5 recordsLinked to original sources

PubMed2006

Visual acuity and optical parameters in progressive-power lenses.

PURPOSES: The purposes of this study are to explore the effect of astigmatism and high-order aberrations of progressive-power lenses (PPLs) on visual acuity (VA) and to find a good optical metric for evaluating visual performance of PPLs. METHODS: A Hartmann-Shack (HS) wavefront sensor was used to measure PPLs and human eyes either independently or in combination. An additional channel permits the measurement of VA under the same optical conditions. Measurements were taken in six relevant locations of a PPL and in three eyes of different normal subjects. In every case, we obtained the wavefront aberration as Zernike polynomials expansions, the root mean square (RMS) error, and two metrics on point spread function (PSF): Strehl ratio and the common logarithm of the volume under the PSF normalized to one (Log_Vol_PSF). RESULTS: Aberration coupling of the PPL with the eye tends to equalize the retinal image quality between central and peripheral zones of the progressive lenses. In the corridor of the PPL, the combination of small amounts of coma, trefoil, and astigmatism (total RMS 0.1 mum) does not significantly affect VA. The continuous increase of astigmatism from corridor to outside zones reduces moderately the quality of vision. The highest correlations between optical metrics and VA were found for Log_Vol_PSF of the entire system eye plus PPL. CONCLUSIONS: Ocular aberrations reduce optical quality difference between corridor and peripheral zones of PPLs. In the same way, VA through the corridor is similar to that of eyes without a lens and it decreases slowly toward peripheral locations. VA through PPLs is well predicted by the logarithm of metrics directly related with image spread (Log_Vol_PSF or equivalent) of the complete system of the eye with the lens.

Adult↗

PubMed2006

An analytical model describing aberrations in the progression corridor of progressive addition lenses.

PURPOSE: In the progression corridor of a typical progressive addition lens (PAL) with an addition of 2.5 D, the power changes by roughly 1/8 D/mm. This renders a power difference of some 0.5 D across a typical pupil diameter of 4 mm. Contrary to this fact, PALs do work well in the progression zone. To explain why, we apply a simple model to derive wavefront characteristics in the progression zone and compare it with recent experimental data. METHODS: We consider a simple analytic function to describe the progression zone of a PAL, which has been introduced by Alvarez and other authors. They considered the power change and astigmatism, which are second-order wavefront aberrations. We include third-order aberrations and compare them with spatially resolved wavefront data from Hartmann-Shack-sensor measurements. RESULTS: The higher-order aberrations coma and trefoil are the dominant aberrations besides astigmatism as given by experimental data. According to our model, the third-order aberrations in the transition zone are strongly coupled to the power change and the cubic power of the pupil radius. Their overall contribution according to experimental data is nicely reproduced by our model. The numeric contribution of higher-order aberrations is small and, for practical purposes, the wavefront can be described locally by the second-order components of sphere and astigmatism only. CONCLUSIONS: We propose a simple analytical model to understand the optics in the progression corridor and nearby zones of a PAL. Our model confirms that for typical pupil sizes, all higher-order aberrations, including the dominant modes of coma and trefoil, are small enough to render an undisturbed vision in the progression zone. Therefore, higher-order aberrations have a minimal impact on the optical performance of these lenses.

Astigmatism↗

PubMed2004

Comparison of aberrations in different types of progressive power lenses.

Recently, computer numerically controlled machines have permitted the manufacture of progressive power lenses (PPLs) with different designs. However, the possible differences in optical performance among lens designs are not yet well established. In this work, the spatially resolved aberrations, at 20 relevant locations, of three PPLs with different designs were measured with a Hartmann-Shack wavefront sensor. The wavefront aberration (WA), its root mean square error (RMS) and the point-spread function were obtained. Spatially resolved plots are shown for all aberrations, astigmatism alone, and for higher order aberrations. The average RMS of all zones is also compared, and the standard deviation is used as a parameter to evaluate the level of hard-soft design. We find differences in the spatial distribution of the aberrations but not in the global RMS, indicating that current PPLs are rather similar to a waterbed, with the aberrations being the water: they can be moved but they cannot be eliminated.

Accommodation, Ocular↗

PubMed2003

Spatially resolved wavefront aberrations of ophthalmic progressive-power lenses in normal viewing conditions.

PURPOSE: To measure the wavefront aberration at different locations in progressive-power lenses (PPL's) isolated and in situ (PPL's plus eye). METHODS: A Hartmann-Shack wavefront sensor was used to measure progressive-power lenses and human eyes either independently or in combination. In each selected zone, the lens was placed and tilted accordingly to simulate natural viewing conditions. We measured 21 relevant locations across an isolated PPL (plano lens of power addition of 2 D). In six of the locations, the wavefront aberration of the eye plus PPL were obtained in two ways: (1) by direct measurement of the system and (2) by adding the individual wavefront aberrations of the eye and the lens for each appropriate zone. In every case, we obtained the wavefront aberration as Zernike polynomials expansions, the root mean square error, the point-spread function, and the Strehl ratio. RESULTS: Along the corridor of the PPL, third-order coma and trefoil, and astigmatism were the dominant aberrations. In areas of the PPL outside the corridor, astigmatism increased, whereas other aberrations remained similar to the lens center. Small differences were found between the direct and calculated methods used to obtain the wavefront aberration of the eye with the lens, and the possible sources of errors were discussed. In some lenses zones, the aberrations of the lens may be compensated by the particular aberrations of the eye, yielding improved optical performance over that present in the lens alone. CONCLUSIONS: We designed and built a wavefront sensor to perform spatially resolved aberration measurements in ophthalmic lenses, in particular in PPL's, either isolated or in combination with the eye. The aberrations appearing in the PPL were compared with those in normal aged eyes.

Adult↗

PubMed2002

Correlation between optical and psychophysical parameters as a function of defocus.

PURPOSE: To evaluate how ocular optical image quality and psychophysical estimates of visual performance compare to each other as a function of defocus. METHODS: We measured the optical modulation transfer function using a double-pass apparatus and psychophysical estimates of visual performance: contrast sensitivity function (CSF) and visual acuity. Both sets of data were obtained under the same optical conditions. RESULTS: We measured optical and psychophysical parameters as a function of defocus. We studied the correlation between optical parameters (Strehl ratio and the logarithm of the volume in the double-pass image [log_Vol D-P]) and psychophysical parameters (the area under the fitted CSF represented in a logarithmic scale with the spatial frequency in linear scale [Area CSF-log_lin] and visual acuity) for different values of defocus. CONCLUSIONS: Strehl ratio is well correlated with the psychophysical estimates of the visual performance for moderate amount of defocus (within 1 D), whereas the other parameter (log_Vol D-P) is well correlated for larger ranges of defocus (within 2 D) and for different pupil diameters. These results suggest that optical measurements could be used for clinical testing of ophthalmic optics.

Adult↗